Mental illness is not the same as a learning disability. Those with a mental illness are usually of normal intelligence, although they may have difficulty performing at a normal level due to the illness.

Schizophrenia affects approximately 1 person in 100.  Symptoms include impairment of thinking, delusions and changes in behaviour.  Its onset is usually in the late teens or early twenties.

The affective disorders are the most common psychiatric disorders.  The primary disturbance is that of affect or mood. These mood disorders may be manic-depressive illness (bi-polar) in which the person swings between extreme high and low moods, or they may be uni-polar in which the person suffers from persistent severe depression.

The causes of mental illnesses are not well understood, although it is believed that the functioning of the brain's neurotransmitters is involved.  More research is needed to determine causes and to plan strategies of prevention.  While the current medications do not cure these illnesses, they can reduce the symptoms for most people.